Lime kiln



April 19, 1960 H. DE w. ERASMUS ET A1. 2,933,297

LIME KILN 2 Sheets-Sheet 1 Filed Oct. 4. 1957 INVENToRs Hendrik de Wef Erasmus By7 Hans Leuenherger 'r role/ver April 19, 1960 H. DE w. ERASMUS ETAL 2,933,297

LIME KILN Filed Oct. 4, 1957 2 Sheets-Sheet 2 l 4 WATER'Ni Iw TER ouT N VEN TORS Hendrik de We? rasmus @y Hans Leuenberger ATTORNEY United States Patent O" LIME KILN Hendrik de W. Erasmus, Lewiston, and Hans Lenenberger, Niagara Falls, N.Y., assignors to UnionCarbide Corporation, a` corporation of New York Appiication october 4, 1957, serial No. 688,815-

s claims. (c1. 263-30) This invention relates Ito a vertical kiln for calcining limestone, and more particularly concerns a lime'kiln having improved means for effecting evenv distribution-of the heat therein.

The present practice of burning limestone is generally accomplished ineither a rotaryvor vertical.. kiln. The rotary kiln is fairly effective, but this type of.furnace-is expensive to install, and in the calcining process considerably more fuel is necessary than inthe `vertical kiln; In thetverticaltypekiln a mixed feed of limestone and coke maybe employed, but this method of burninglimestone is effective only ifthe solid fuel isawell distributed. A prime disadvantage of mixed feed kilns isV that inV many cases :the residual ash from the coke becomes an objectionable'part of the final product. In addition, coke may beV a more expensive fuel than available gaseous or` liquid fuels which have the additional advantages of low sulfur. and no ash content.A y

In. the past several attemptsrhave been made' to burn.l limestone in a vertical kiln using uid fuels, such as com.- bustible liquid or gaseous fuel mixtures. Suchattempts have not been generallyl satisfactoryzdue to the high llame temperatures produced by the combustion of the fluid fuel.

One ofthe principal problems in fluid-fired kilns concerns the diiliculty in obtaining uniform distribution. and mixing of the air and fluid fuel in the calcination zone of the kiln. It frequently happens that combustion of lluidfuelrnixtures may be more completeV -in one section ofthe kiln than inb another. The result is that in some sections of the kiln the material to be treatedisoverheated and becomes fused, andl forms into agglomerated` masses known as hangs," while in other sections of :the kiln the t limestoneis only partially burnt in its downward travel,

resulting in a high core content of unburnt limestone in:

the product. Y p

In conventional vertical kilns, refractory ducts aregenerally used to introduce the fluid fuel as uniformly as possible. throughout the cross section of the calciuation4 zone. Being stationary, these refractory ducts tend: tof

be heated to higher temperatures thanthe passing par-4 tially or completely burned lime, with` the result that the limetends to stick to the refractory structure, causing progressive build-up or hangs in the kiln. Such hangs disturbthe uniformity of the flow of solids, whichin turn.

results in poor average quality. Also, if` not quickly removed, they cause severe damage to the Vrefractory structure in the kiln. This is a frequent occurrence, since hangs are not easily detected inside the kiln.

It is, therefore, an important object of the present in-` vention to provide an improved lime burning kiln, whereinthe difficulty of maintaining and'controlling theV calcination temperature is to a large degree avoided, and wherein an even distribution of fuel and air throughout the calcination zone may be effected.

Another object is the provision of a networkof conduits and ducts so constructed andfarranged' as to intro-l duce` combustible fuel mixtures and air into the calcining zone and to complete the combustionoflsaid mixtures-in 2,933,297l `Patented Apr. 19,. 11960 ice y several stages, thereby insuringthe even distribution of heat throughout the calcining zone.

To the end that the above set forth dihiculty may be resolved, ythe present invention contemplates an improved lime burning kiln, wherein water-cooled beams are cmployed instead of refractory Vducts tointroduce: and distribute the uidfuel in the kiln, and wherein the watercooled beams are run horizontally; through various portions of the kiln, over and` around which the limestone and lime travel in their downward descent.` This move# ment allows a V-shaped void (free of lsolid material) to formunder eachbeam. The-voids permit visual obscrv ance of the movement of the limestone clear across the entire kiln at several levels. Hangs can thus be easily detected, and the uniformity of' the: firing observed.

Bymeasuring the temperature rise of the water usedAto coolthe` beam sections, the result can be correlated with" the temperature of the charge. If the water temperature indicates excessive heat concentration inside a particularl areaxof the kiln, remedial stepsmay be quickly taken to change and control the temperature of the charge so as toproduce an adequately calcinated limestone without hangs.

According to the present invention, the burning of.

limestone and other materials may be carried out in a vertical' kiln, using uid combustible fuel, without.V encountering the prior art diiculties of uneven heat distribution resulting in unavoidable sintering orY incompletel calcination ofthe limestone. The method of the inventionzgenerally consists in'A burning crushed limestone in a vertical kiln wherein; combustible mixturesof fluid fuelE andzprirnaryairareintroduced and distributed through-- out the entire cross` section of the calcination zone in the? kilns usingfwater-cooled beamsV as conduits todistributeV thefuel mixtures. The'4 heat of combustion of these fuel mixtures is` disseminatediin4 several stages by providing anvamount of primary airinsulicient for the complete' the desiredtemperature` range of between 1300 C. and" 1400o C. Secondary additions of air, introduced in an',

adjustableamounts near the lowerr end of the kiln and uniformly distributed across the kiln, are preheated by the hot` descending limeproduct, and `caused to mix with the aforesaid gases `toprovide secondary combustion reactions in'thefregion of thefkiln slightly above the region of pri-` mary combustion. By providing a quantity of secondaryairgreatly in excess ofth'at` required forrburning the combustible gases, the temperatureofsecondary combustion canzbeiconnedto within thedesired Vacceptable limits.

Thereafter, becauserofthelheat.supplied by the rising gas* products of combustion fromA below, at higher levels in thefcalcinationf zone, thev primary air-fuel mixture may, if t desired, be` progressively diluted with recycled gasA productsofcombustion, using an excess of uid fuel so asto.. produce aprimary and secondary combustion temperature substantially the same as the temperature below. In?A thisY manner an even. distributionV off` heat throughout theentire calcinationzone ofthekiln may be obtained.

The invention alsoA consists in a uid fuel operated verticaln kiln adapted to fulfill the aforesaid method,

whichlcomprisesa hollow vertical shaft kiln having at thel topsuitable accessories for introducingV the limestone material to betreated and for removing the gas products,` of combustion, and chutes at the bottom of the kiln for l cooling and removing lime product and means for unfrmly admitting :secondary air across theflower end of the kilndfor preheating the secondary air by contact withy the'jemerging--limeproduct.' A plurality of horizontal.` Water-cooledb'eams; vertically and horizontally spacedv from: eachA other andldisposed' in' staggeredl relation' distributing the primary air-fuel mixtures to effect a substantially uniform temperature of calcination in accordance with the principles of the invention. The ducts further Vprovide novel means for visually inspecting the progress of calcination inside the kiln.

The invention is illustrated by way of example only in the accompanying drawing in-which: Figure l is a sectional elevational view illustrating the principles and features of the present invention;

Figure 2 is a sectional view of the apparatus shown in Figure 1 taken along theline 2-2; f

Figure 3 is an enlarged sectional view of the water cooled, gas dispensing beam employed in the present invention, taken along the line 3--3 in Figure 1;

Figurez4 is a sectional view taken along line 4--4 in Figure 3; and v Figure 5 is an enlarged sectional view of the off-take pipe taken along line 5-5 in Figure 1.

Shown in Figure l is a limeburning kiln V10 embody-ing the principles of the present invention, and comprising a vertical shaft 12 of rectangular cross section provided with end walls 13, 14 and a refractory lining 15, 16 therefor, and having conventional charging chutes 17 at the top of the kiln for the introduction of the material to be treated. Discharge chutes `18 at the bottom of the kiln permit the removal of lime product, provision being made for thepassage of secondary air upwardly into the kiln shaft in order'to simultaneously preheat the air and cool the emerging lime product. The secondary air may be introduced either upwardly through the chutes 18.or preferablyvrby means of a' transverse oriced air duct-Orgtubes 70, to be described hereinafter.

l In accordance. with the invention, novel means of tempering the gases of combustion inthe calcining zone make possible 'the calcination of'limestone and other materials `under carefullycontrolled temperature conditions VFor the accomplishment of this purpose there is provided a plurality of high strength structural beams 20, made of steel or other temperature-resistantV material extending horizontally across the'calcining zone, and supported at opposite ends by the end walls 13-'13, the beams extending'outwardly beyond said walls. These beams are vertically and horizontally spaced from each other, and disposed in staggered relation in order to provide channelsV affordingmaximum distribution of the fuel` mixture in V.the kiln. Any number and arrangement of beams may be employed in the practice of the invention, ve beams disposed in staggered arrangement and in two rows Vat different levels, no beam being vertically aligned with another beam, being shownand illustrated herein. Y t

Each of the beams 20 is preferably a wide flange beam having a vertical web 22A provided with laterally extending upper flanges 23, 24 and lower flanges 25, '26. The'ends of theflanges 23, 24, carry short extensionmembers or lips 23a, 24a, which project laterally fromthe underside of the ilanges, and4 slightly beyond the laterall extremities thereof. Similar flange members 25a, 26a, joined to the topside of lianges 25, 26, terminate flush with the lateral ends of their respective flanges. Welded to the ange members 23a, '2411,4 25a and 26a, and to the central web 22, are rectangularv duct plates 23b, 24b,-25b and 26h, respectively, to form therewith longitudinal, rectangularly cross sectioned, cooling ducts 28, 29, 30 and 31 for cooling the beaml 20. Side walls 33 and34 connect the lateral extremities of the duct plates to form longitudinal passageways 35 and 36 for conducting gases into the kiln. These side walls 33 and 34 may be provided with longitudinal, cooling ducts 38, 39, 40 Vand 41, similar to ducts 2-8, 29, 30 and 31.- Cooling .water may be passed in series through these ducts by water tight connectors or loops 43 between adjacent ends of the longitudinal ducts to provide a continuous serpentine path for the circulation of water therethrough. Thus, cooling Water supplied to duct 28A passes sequentially through ducts 38, 39, 30, 3,1,

m41, 40 and leaves through duct 29. A comparison of the 4entering and exit temperatures of the cooling water gives a fair indication`of the temperature conditions inside the kiln, and is an excellent and convenient means for ascertaining the uniformity of the temperature in a number of regions inside the kiln. 'Ihe connectors 43 may be made detachable so that individual beam units may be conveniently withdrawn for repair or replacement.

Calcination is accomplished by means of combustible fuel mixtures which are drawn into direct contact with the material in the calcination zone through one or more combustible fuel lines or pipes -45 having longitudinally spaced and laterally extending outlet ports 46. The exiting fuel from the fuel outlets 46 enters the calcination zone through slotted openings 48 in the side Walls 33, 34, the total cross section of these openings being less than or equal to 60 percent of the total cross sectional areauof the passageways 35, 36, not occupied by the fuel lines 45, Any suitable number and arrangement of vfuel linesv 45, outlets 46 and slotted openings 48 may be used, the lines 4'5 being shown and illustrated herein in vertically spaced tiers in each passageway, and supportingly held therein by pipe supports 50. As here illustrated in Figure` 1, the fuel lines 45 may be blind end pipes dis-l posed in duplicate pairs in each passageway, each pair being adapted to introduce combustible uid fuel at spaced intervals as far as the center of the calcination zone of the kiln. The openings 48 are shown in registry with'the outlets 46, but obviously other and different; arrangements may be equally as feasible.

It should be noted that in the specific construction il-z lustrated in Figure 3, there is a possibility of obstructing the openings 48 with limestone andV thereby impairing the functioning of the fuel distribution system of the invention. To avoid this possibility, each of the lips 23a, 24a should have enough of an overhang to provide a sufcient angle of repose so that freely flowing streams of combustible fuel mixtures through the openings 48 are assured at all times.

Controlof the combustion temperature of the ejectedv fuel in pipes 45 is achieved in the present invention by utilizing ythe space within the passageways 35, 36 not occupied by the fuel lines `45 as additional conduits 52 for the admission of either` air'or diluent gases such as recycled products of combustion. These conduits 52 may be compartmentalize'd if so desired to avoid mixing of the iluids admitted from opposite ends of the beam 1270,' thereby further ensuring even distribution of the fuel. Inasmuch as complete combustion of the fuel in the line 45V will result in temperatures greatly in excess of 1400? C., the fluids in fuel line 45 and conduits 52 may be` admitted into the calcinationzone through the slotted` openings 48 in such proportions as to limit the amount: of primary oxygen that is made available to the fuel, so that combustion of the fuel mixture may be distributed into several stages of combustion. For this purpose the fuel mixture admitted into the lowermost level of the Y clcining zone'l may comprise an excess of fluid fuel with suflcient oxygen-bearing gases to give a flame temperature of about 1400 C. in the 'immediate vicinity of the lower beams The iuid fuel which is only partially burnt due to the controlled oxygen deciency in this primary stage of combustion, is then available for'admixture and secondary combustion with the ascending preheated air from secondary air tubes 70. lThe additional flame brought about by secondary combustion will `producel only a moderate rise in temperature, due to the limited onlcentration of combustible gas in this partially burnt In the meantime, primary combustion of excess fuel and oxygen-bearing` lgas at the upper beam level also produces a temperature of approximately l400 C., thereby making available additional partially burnt fuelzfor the-remaining oxygen in the ascending preheated air.Y

Vlvxgcessive temperature rise at this upper level s fur-. l

titer inhibited dueto the limited amount `i remaining .combustion Vfrom the lower combustion level. AAs a consequence, the combustible fuel mixturesl obtained from i -ilines 45 and conduits 52 are controllably released in sev- `eral stages of combustion, so that at no point in the cal- ..cination zone is `an excessive temperature condition encountered.

It should be understood that although the ,burning process as described hereinabove has been simplified for purposes of expansion and illustration, the fuel mixtures may be burned in anyl number of stages, or may be only `partially burned if so desired. As a practical matter, the `fuel should be burned to completion by the time it reaches .these fluids be cleansed of impurities to prevent the `choking and clogging of the fuel distribution system.

For this purpose, the fuel and/or air and/or recycled products of combustion may be thoroughly cleansed in a -Venturi type scrubber, for example, a Pease-Anthony scrubber. Fluids cleaned in this manner and employed in the practice of the, invention are clear and colorless. In actual analyses of 100 cu. ft. samples` of these purified uids, weighable amounts ofimpun'tes could not be detected.

. lAn obvious advantage of the water-cooled beams 20 `is that Vthey affordnovel `means for visually inspecting the calcination zone of the kiln from a vantage point outside'the kiln. The square crosssection of the beams 20 .allows a V-shaped void 62 which runs horizontally across `the kiln, to be formed :directly below the beam. Through sight holes or windows 64 disposed in the walls 13 in registry `with the voids 62, preliminary signs indicating the `formation of incipient encrustations, such` as the ame coloring of the kiln charge, may be observed at several levels across the entire kiln without interference from supporting columns. .Hangs can thus be easily detected, and the uniformity of the firing observed.

When the formation of a hang is detected, the mass of accumulatedflimestone may be broken up into smaller `pieces and made to move along with the limestone charge by means of probing tools (not shown), such as stoker bars, vpneumatic drifter drills or other power devices. The probe tool may be loosely inserted in an elongated probe hole 66 in the end wall 13 slightly above the beam 20, and manipulated in an arc along the top of the beam :flanges 23, 24, so as to disintegrate the hang and to free the beam `of any encrustations which might serve as nuclei for future hangs. Bythe use of drifter drills, it is possible toeiciently operate kilns Vof much larger cross section than heretofore.

To remove the gases of combustion, the upper por- `tion of the shaft 12 may be provided with one or more suitably formed off-take tubes or pipes, such as inverted trough-like conduits and preferably in the form of cylindrical olf-take pipes 54 horizontally spanning .the shaft 12 and extending outwardly beyond the walls 13-13. As illustrated here in Figure 5, suitable apertures 55 in the lower halves of the pipes .54 serve as inlets for admitting gas from the upper end of the shaft.

As a feature of the invention, the efficiency of the exhaust gas removal from the kiln is considerably enhanced `by the attachment of skirts or side plates 56, tangentially secured in pairs to opposite sides of the offtakepipes 54, and depending therefrom. Since the pressure of the limestone moving downward might tend to fold these skirts inward, brace bars 57 secured to the lower ends of each pair of plates 56 are employed to hold them separated and in a verticalposition.

The skirt attachments thus permita largeriarea from which the gas -may be Awithdrawn through the apertures 55. A substantial reduction `is thus made in the `exhaust gas `velocityfrom the bed of limestone.

With the'abovearrangement the offtake pipes 54 eliminate the exhaust gases by suction through a suction `blower (not shown) in a manifold 60. A portion of the combustion products in the manifold 60 may be recycled to a lower portionV of the calcination zone, or into the passageways 35, 36 in the beams 20 through a valve- .controlled, return line 61 to further control and modify the flame temperature inside the calcination zone.

In theevent the exhaust gases are to be recycled, suitable dust-removal equipment of the type discussed herein above should, of course, be providedV to remove the entrained dust.

, As previously mentioned, a further feature of the inven- ,tion resides in the employment of multiple air tubes 70 `horizontally mounted across the kiln in a manner similar to beams 20 and disposed slightly above the discharge chutes 18. The air tubes are connected to a source of air (not shown) and are provided with a series of horizontallyspaced apertures 72 for supplying secondary air to the kiln. A slide 74 disposed inside the tube 70 and havingapertures in registry with the apertures 72 serves to adjustably control the size of the aperture openings 72. In this manner an adjustable and uniform distribution of secondar,l air across the kiln may be eifected.

By way of amplifying the above procedure, the following example illustrates again the multi-stage combustion progress in the lime kiln of the present invention. At the lower level of beams 20, enough excess carbon monoxide furnacegas may be mixed with air-bearing products of combustion containing about 14% oxygen through the mixing ducts 45 and 52, to give a flame temperature of about 1400 C., and produce first stage products of combustion containing about 10% carbon monoxide. When this mixes with the preheated air supplied by air tubes 70 Yand travelling up the kiln, the additional flame resulting from secondary combustion will only be about 500 hotter than the preheated air. If the volumes of preheated air and first stage products of combustion are equal, then the-second stage products of combustion will contain approximately 8.2 percent oxygen. At the upper level, a mixture of air and recycled combustion products containing about 16% oxygen may also be burned with furnace gas to give first stage products of combustion containing` 16 percent carbon monoxide and a llame temperature of approximately 1400" C. When these first stage products of combustion from the upper beam level mix and react with the ascending second stage products of combustion from the lower beam level containing 8.2 percent oxygen, the maximum temperature rise will again be less than 500 C. above the surrounding limestone.

To indicate the practicability of the invention, a kiln constructed according to the prior art for an output of 3A ton per square foot of kiln cross section per day was converted into one having the water cooled, fuel distributing beams and secondary air tubes of the invention, the converted kiln having a forced draft of approximately 1.0 p.s.i. Results of a number of tests showed a distinct improvement in kiln e'lciency and lime quality, the output of the converted kiln averaging approximately three tons per square foot of kiln cross section Vper day. In other applications of theiteachings of the invention, lime withdrawal rates as high as approximately four tons per square foot per day have been obtained compared to the standard withdrawal rate of approximately two tons per square foot per day.

From the above disclosure it will be seen that the beams serve as excellent devices for the equal dispersion of fluid fuel mixtures throughout the calcination zone of the kiln. Any alteration in the amount of oxygen-bearing gas or fuel to aect the ame temperature may be easily made. As a resulttl1e-surfaceslof the beams are exposed to vtemperatures of a magnitude at which reaction with the .material in the kiln would normally be possible. .ever, this objectionable possibility is'oifset by the water- Howcooling inside the surfaces of each of the beams.

Although'the construction of the kiln makes possible Ithe use of limestone as the charge with a fluid fuel, it is to be understood that it need not be so limited, since the flexibility of operation of the kiln of the present invention permits the substitution of coke for any portion vof the fuel. In the event of such substitution, the coke could be initmately mixed with the limestone, and thus the coke-to-fuel ratio could be proportioned tov any degree, its use 'being dependent only uponthe availability Yand economics of the material in the Yarea of use. Furthermore, the operation of the kiln of the V`present invention is not necessarily limited to the calcination of limestone.

.Other calcining operations such as that performed on dolomite may be carried out in the kiln of the present invention in accordance with the principles thereof, if so desired. Y

By fluid fuel as deiined hereinabove is meant either a gas such as carbon monoxide, or any number of uids which are commonly employed in a'fuel capacity, such as conventional oil and gas fuels.

It will be understood'that modifications and variaftions maybe effected without departing from the spirit and scope of the novel concepts of the present invention.

This `application is a continuation-in-part of our co- .'pending application, S.N. 551,600, iiled December 7, 1955, now abandoned. Y

What is claimed is:

l. A kiln for Athe production of lime from limestone comprising a vertical shaft having a feed zone in the upper portion thereof through which a charge is introduced for passage downwardly through the shaft, a calcining zone in said shaft below the feed zone and in which said charge is heated to form lime, and a cooling zone in the lower portion of the shaft below said calcining zone for receiving product from said calcining zone yand from which said product isdischarged from said shaft, means for'introducng air into the lower end of the shaft to rise successively through at least'the cooling zone and the calcining zone so as to cool the prod- `uct and at thesame time preheat the air before it passes into the calcining zone, a plurality'of horizontal hollow beam members extending across the calcining zone, each having oppositely disposed lateral openings alongV the length of the beam, means within the beam for delivering a mixture of fuel and primary combustion air, in a proportion in which said air is less than that'required for complete combustion, to said lateral openings for discharge therethrough in substantially uniform distribution along the length of the beam, whereby primary partial combustion of the fuel and combustion air supplied through the hollow beam members occurs in the vicinity of the .beams and the unburned portion of fuel supplied therethrough isconsumed by contact with the preheated air rising through the charge to evenly distribute heat throughout the calcining zone.

2. A kiln for the production of lime from limestone comprising a vertical shaft having a feed zone in the upper portion thereof through which a charge is introduced for passage downwardly through the shaft, a calcining zone in `said shaft below the feed zone and in which said charge is heated to form lime, and a cooling zone in the lower portion of the shaft below said calcining zone for receiving product `from said calcining zone and from which said product is discharged from said shaft, means for introducing air into the lower end of the shaft to rise successively through at least the cooling zone and the calcining zone so as to cool the product and at the same time preheat the air before it passes into the calcining zone, a plurality of horizontal hollow beam members extending across the calcining zone, each having oppositely disposed lateral openings along the length of the beam, uid fuel conduits and primary conibustion air conduits located within said beams, saidrconduits having outlets positioned to dischange fuel and Vair mixtures through said openings in substantially uniform amounts along the length of the beam. I

3. A kiln for the production of lime from limestone comprising a vertical shaft having a feed zone in the upper portion thereof through which a charge is introduced for passage downwardly through the shaft, a calcin- .ing zone in said shaft below the feed zone and in which said charge is heated to form lime, anda cooling zone in the lower portion of the shaft below said calcining zone for receiving product from said calcining zone and from which said product is discharged from said shaft, means for introducing air into the lower end of the shaftto rise successively through at least the cooling zonev and the calcining zone so as to cool the product and at the same time preheat the air before it passes into the calcining zone, a plurality of horizontal hollow beam members extending across the calcining zone, each having oppositely disposed lateral openings along the length of the beam, fluid fuel conduits and primary combustion air conduits located within said beams, said conduits having outlets positioned to discharge fuel and air mixtures through said openings in substantially uniform amounts along the length of the beam, said hollow beam members having a plurality of longitudinally -extending ducts for the circulation therethrough of cooling water.

4. A kiln for the production of lime from limestone comprising a vertical shaft having a feed zone in the upper portion thereof through which a charge-is introduced for passage downwardly through the shaft, a calcining zone in said shaft below the feed zone and in which said charge is heated to form lime, and a cooling zone in the lower portion of the shaft below said calcining zone for receiving product from said calcining zone and from which said product is discharged from said shaft, means for introducing air into the lower' end ofthe shaft to rise successively through at least the cooling zone and the calcining zone so as to cool the product and at the same time preheat theair before it passes into the calcining zone, a plurality of horizontal hollow beam members extending across the calcining zone in at least two horizontal rows, said members being spaced insaid rows in a staggered relation to distributeiiuid fuel throughout the cross section of the calciningzone of said shaft, each beam member having oppositely disposed lateral openings along the length of thebeams communicating with the interior of said beams, ,1a plurality of combustible uid. fuel conduits in said beam, .each conduit extending to different positions along the length ofthe beam for providing uniform delivery of said fluid fuel along the length of the beam, said fuel conduits having outlets positioned to discharge through said openings, the remaining space in said hollow beam constituting a conduit for the flow of primary combustion air into said lateral openings for discharge therethrough in substantially uniform amounts along the length of the beam, said hollow beam members having a pluralityof longitudinally extending ducts for the circulation therethrough of cooling Water.

5. A vertical kiln for the production of lime, comprising a hollow shaft havinga calcining zone, aplurality of channels acrosssaid shaft and within thelcalcining zone, each of said channels comprising a vertical web portion4 having at the upper and lower end thereof a pair of laterally outwardly extending anges, a pair of laterally spaced side walls on opposite sides `of said web and connected to the outer portions of said Aflanges to form a pair of longitudinal passageways straddling said web, each passageway having therein a pair of longitudinal ducts disposed respectively Yadjacent'said upper and lower anges, and a pairof longitudinal ducts'disposed adjacent the sidewall thereof, aconnection betwsenfadjacentends of said longitudinal ducts to provide film-m a continuous serpentine path for the circulation of cooling water through said ducts, a plurality of openings in each of said passageways communicating with the interior of said shaft, a plurality of combustible fluid fuel lines in each of said passageways, said fuel lines having outlet portions in the vicinity of said openings respectively, the space in each of said passageways around said fuel lines constituting a conduit for the ow of oxygenbearing diluent gases into the interior of said shaft through said passageway openings for controlling the heat of combustion resulting from the mixture therewith of the fuel from said rfuel lines.

References Cited in the le of this patent UNITED STATES PATENTS Stetefeldt June 14, 1864 Greenawalt Feb. 15, 1938 Azbe Oct. 15, 1946 Bergstrom Aug. 10, 1948 Vogel Mar. 12, 1957 FOREIGN PATENTS France June 3, 1938 

